Crankset with no neutral position

ABSTRACT

The crankset for the driving of bicycles and other vehicles or machines by muscular force includes two coaxial crank spindles (8, 9), mounted in a bottom bracket tube and each provided with a radial arm (20, 22) beside one or more toothed chain rings driving a chain transmission. The chain ring carrier (15) has an axis (25) offset forwards with respect to the spindles and it is coupled to each radial arm by an articulated connecting rod. Sealing gaskets (42, 46, 53) are placed within the bottom bracket tube (2) and between both spindles to protect the spindle bearings (41, 45, 48, 51) as regards the exterior. The chain ring carrier (15) is mounted by sealed roller bearings (27) on an adjustable eccentric member (26) to adjust the direction of eccentricity. The two articulations (34) of the connecting rods on the chain ring carrier can be situated substantially facing the respective cranks (11, 13).

FIELD OF THE INVENTION

The present invention concerns a crankset without a dead centreposition, in particular for a bicycle, including: a fixed bottom brackettube, a hollow outer spindle rotatably mounted about a first axis byfirst bearings in the bottom bracket tube and attached to a first crank,an inner spindle rotatably mounted by second bearings coaxially in theouter spindle and attached to a second crank, sealing means for assuringsealed protection of the bearings as regards the exterior of thecrankset, an output member rotatably mounted about a second axisparallel to and offset with respect to the first axis on an eccentricmember fixed to the bottom bracket tube, the output member beingintended for driving a mechanical transmission, and two articulatedlinkages connecting the output member respectively to each crank or toeach spindle.

The invention applies in particular to bicycle cranksets, but also toany other use of a crankset driven by muscular force, for example forpropelling any vehicle or for activating a machine, a ventilator, anelectric generator, etc.

BACKGROUND OF THE INVENTION

In a conventional crankset, the vertical position of the cranks in asame radial plane constitutes a dead centre position, because the weightof the person pedalling cannot produce a torque on either of the twocranks in this position. In order to overcome this drawback, it has beenproposed for more than 60 years to put the toothed chain ring, whichdrives a bicycle chain, forwards in an offcentre position, to separatethe cranks from each other and from the chain ring in order to allowthem mutual angular play, and to connect each crank or the spindlethereof to the chain ring by an articulated linkage able to absorb theradial movements due to the eccentricity. FR Patent Nos. 763,303,905,476, 984,583, 2,526,392 and 2,584,671, and U.S. Pat. Nos. 4,159,652,4,772,252, 4,816,009 and 5,067,370 disclose such cranksets without adead centre position. Patent application WO 95/19909 also discloses sucha crankset, further including an oscillating support which carries thecrank spindles to allow the eccentricity value to be modified betweenzero and discreet different values, when it is moved by means of acontrol lever.

However, none of these cranksets has made any commercial impact,probably because of manufacturing problems and problems of water anddirt resistance, since sealing is difficult to assure because of themultiplicity of moving parts.

For conventional gear and crank apparatus with a single spindle, knownexamples of annular sealing gaskets are illustrated in GB Patent No. 2135 399 and FR Patent No. 2 616 493.

In a crankset of the kind indicated in the preamble, disclosed in Patentapplication WO 86/05459, each of the two articulated linkages betweenthe corresponding spindle and the chain ring acting as output memberincludes a radial arm made integrally with the spindle and oriented inthe same direction as the corresponding crank. In order to transmit anapproximately tangential force and thus a torque to the chain ring, thelinkage includes either a roller carried by the chain ring and engagedin a radial slide of the arm, or an oscillating disc housed in the armand provided with an eccentric pin engaged in the chain ring. Thisarticulated mechanism is protected, on the outer side of the chain ring,by a circular housing fixed to the chain ring, having a frontal flangeprovided with a central opening for allowing the inner spindle carryingthe crank on that side to pass. This opening is large enough to allowthe oscillating rotating movement of the housing with respect to thespindle, because of the eccentricity; it is obturated internally by aflange integrated with the spindle, a sealing gasket in the shape of anannular disc being placed between the two flanges so as to slide ontoone of them. A portion of the sliding surface on this flange is thussometimes covered by the gasket and sometimes exposed to the open air.Dirt which reaches this surface can thus be introduced into the joint,rapidly deteriorate the sealing, reach the bearings and damage them,which has led to marketing of this type of crankset being abandoned. Thelatter also had the drawback of the transverse space requirement of thehousing containing the two radial arms between the chain ring and thecorresponding crank, requiring the other crank also to be moved away tomaintain the symmetry with respect to the median plane of the bicycle.

SUMMARY OF THE INVENTION

The present invention concerns a crankset capable of avoiding theaforementioned drawbacks, while assuring durable sealing of the spindlebearings, which are generally rolling bearings, and allowing compact andlight construction. An additional object is to arrange the articulatedlinkage in a simple, efficient form resisting external ambientconditions. Another additional object is to arrange the articulatedlinkage so as to obtain optimum transmission of the driving torque tothe output member when such driving torque is at maximum, i.e. when thedescending crank is approximately horizontal.

Generally, the invention concerns a crankset of the type indicated inthe preamble, characterized in that the sealing means include firstsealing means, disposed around the outer spindle in the bottom brackettube and protecting the first bearings as regards the exterior of saidtube, and second sealing means, disposed in the outer spindle andprotecting the second bearings as regards the exterior of said spindle.

Thus the rolling bearings of the crank spindles, which are the elementsmost sensitive to dirt, can be protected by sealing gaskets situatedentirely within the bottom bracket tube, radially between coaxial partsone of which can rotate with respect to the other, in particular betweencylindrical surfaces of these parts. These gaskets may be of a known andwell tested type, occupying little space and providing satisfaction inconventional cranksets. There is no need for an external housing, eacharticulation of the articulated linkages being easily able to berealized by a sealed bearing, available on the market.

Preferably, the second sealing means include an annular sealing gasket,which obturates an annular gap between the outer spindle and the innerspindle on the side of the second crank, and closing means whichobturate in a sealed manner a central bore of the outer spindle on theside of the first crank. These closing means may be formed for exampleby a sealing plug, or by the bottom of said bore if the latter is blind.

In a particularly advantageous embodiment of a crankset according to theinvention, each of said articulated linkages includes a connecting rodhaving one end connected to the output member by a first articulation,the other end of said connecting rod is connected to the correspondingspindle or to the corresponding crank by a second articulation, and saidfirst articulation is situated in proximity to a radial plane passingthrough the first and second axis when the corresponding crank is in adescending horizontal position. This results in facilitated constructionand improved efficiency of the crankset.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will appear in thefollowing description of a preferred embodiment of a bicycle crankset,given by way of example with reference to the annexed drawings, inwhich:

FIG. 1 is a perspective view of the bicycle crankset according to theinvention,

FIG. 2 is a lateral elevation view of the crankset,

FIG. 3 is a cross-sectional view of the crankset along line III--III ofFIG. 2,

FIG. 4 is an elevation diagram showing eight successive positions of thecranks of the crankset,

FIG. 5 shows the evolution of the torque transmitted to the toothedchain rings over one revolution of the crankset, when the cyclist exertssolely a vertical descending force on the pedals, and

FIG. 6 shows the evolution of the rotational speed of each crank overone revolution of the crankset, for a constant speed of the toothedchain rings.

DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to FIGS. 1 to 3, crankset 1 includes a bottom brackettube 2 which is incorporated in a bicycle frame 3, this frame includingtubes 4, 5, 6 and 7, one end of each tube being welded to tube 2. Anouter spindle 8 and an inner spindle 9 are rotatably and coaxiallymounted in tube 2 so as to rotate about a first axis 10. A left crank 11provided with a pedal 12 is removably fixed onto outer spindle 8, and aright crank 13 provided with a pedal 14 is removably fixed onto innerspindle 9. On the right side of the bicycle, crankset 1 includes a chainring carrier 15 on which, in a conventional manner, are mounted forexample three removable toothed chain rings 16, 27 and 18 for drivingthe back wheel of the bicycle by a chain transmission. The chain ringsare fixed by means of screws 19. In a radial plane situated betweenchain ring carrier 15 and right crank 13, outer spindle 8 has a radialarm 20 whose free end is connected to the chain ring carrier by anarticulated connecting rod 21. Likewise, inner spindle 9 has a radialarm 22 whose free end is connected to the chain ring carrier by anarticulated connecting rod 23. Arms 20 and 22 extend in approximatelyopposite respective directions, but oscillating angularly with respectto each other during rotation of the crankset, as do the cranks.

In FIGS. 2 and 3, it will be noted that chain ring carrier 15 is mountedin an eccentric manner with respect to crank spindles 8 and 9, its axisof rotation 25 having an eccentricity E with respect to axis 10 of thespindles. Chain ring carrier 15 is mounted on a stationary eccentricmember 26 by means of a pair of ball bearings 27 centred on axis 25.Eccentric member 26 has a cylindrical end portion 28 centred on axis 10and provided with an outer threading allowing it to be screwed into acorresponding threading of bottom bracket tube 2. End portion 28 alsocarries a lock-nut 29 which is blocked by screwing against tube 2 toblock the angular position of eccentric member 26. Thus, by unscrewinglock-nut 29, it is possible to cause eccentric member 26 to rotate toorient eccentricity E in any desired direction. This direction ishorizontal forwards in the example shown. Consequently, in a knownmanner, when one of cranks 11, 13 is situated in the vertical planepassing through axis 10, i.e. at its dead centre position, the othercrank is situated forward of this plane and can produce torque, as willbe explained with reference to FIG. 4.

In FIG. 3, connecting rods 21 and 23 are not shown, in order to clarifythe drawing and let the construction of their articulations appear. Thearticulation of each connecting rod 21, 23 on the corresponding arm 20,21 is achieved by a sealed rotating roller 31 whose spindle 32 is fixedin the arm by means of a blocking screw 33. Roller 31 is driven into acorresponding orifice of the connecting rod. Articulation of eachconnecting rod onto chain ring carrier 15 is achieved by another sealedrotating roller 34 whose spindle 35 is threaded and held in an orificeof the chain ring carrier by means of a threaded socket 36. Rollers 31and 34 may be for example of the type KR19C.DZ by FAG GmbH ofSchweninfurt, Germany. The two connecting rods 21 and 23 have the samedimensions, and their articulations formed by the two rollers 34 ontochain ring carrier 15 are diametrically opposite with respect to axis25.

FIG. 3 also shows the construction within bottom bracket tube 2, whichis threaded internally at its two ends for accommodating respectivelyeccentric member 26 on the right and, on the left, a externally threadedsocket 38 capable of being blocked by means a lock-nut 39 similar tolock-nut 29. Socket 38 has three inner bearing surfaces of steppeddiameters for centring respectively a first tubular spacer 40, one ortwo ball bearings 41 carrying outer spindle 8, and an annular sealinggasket 42 of the same type as those used in conventional bicyclecranksets. Spindle 8 is fixed axially onto bearings 41 by means of acirclip 43 and a washer 44 held between the inner ring of one ofbearings 41 and a shoulder of the spindle. The outer ring of the samebearing 41 abuts axially against the first spacer 40, whose other endabuts against end portion 28 of eccentric member 26. On the right, outerspindle 8 is supported in eccentric member 26 by another bearing, formedby a needle roller bearing 45 obturated externally by an annular sealinggasket 46 similar to gasket 42.

A central bore 54 passing through the entire length of hollow outerspindle 8 has three successive stepped diameters the smallest of which,opening out on the side of first crank 11, forms an access hole allowingpassage of a screwdriver. When in service, this hole is obturated by aremovable sealing plug 47. The rest of bore 54 contains inner spindle 9and its bearings. These latter include on the one hand, one or two ballbearings 48 whose inner rings are blocked on one end of inner spindle 9by gripping by means of an inner washer 49 and a screw 50, and on theother hand, two needle roller bearings 51 separated by a second spacer52 and protected from the outside by an annular sealing gasket 53obturating the radial gap 59 between the two spindles.

However, it will be noted that the rotatable assembly of inner spindle 9in outer spindle 8 could be achieved in a different way. For example,bore 54 of spindle 8 could be blind, so that the spindle itselfconstitutes a sealed closure of this bore on the side of first crank 11.In order to block the bearings axially between the two spindles, screw50 could pass through inner spindle 9, or the left end of spindle 9could have a radial flange against which the bearings are pressed bymeans of a ring placed to the right of these bearings and pushed againstthem by right crank 13 when it is fixed onto its spindle. Moreover, itwill be noted that the number and the type of roller bearings 48 and 51can be different to that which is described hereinbefore.

Thus, the two spindles 8 and 9 are mounted in a perfectly rigid mannerwithin bottom bracket tube 2, whereas sealing of their bearings isentirely assured by the closure of bore 54 on the left and by annularsealing gaskets 42, 46 and 53 radially gripped between two coaxialcylindrical surfaces. These gaskets have relatively small diameters andare well protected in the bottom bracket tube, which assures a longlifetime.

Furthermore, the construction described hereinbefore allows the cranksetto be assembled in advance, outside tube 2, then mounted as a block insaid tube. Assembly is effected as follows:

each roller 31 is driven into the corresponding connecting rod 21, 23.

spindle 32 of each roller 31 is engaged into the corresponding arm 20,22 and blocked by means of screw 33.

two roller bearings 27 are driven into eccentric member 26.

chain ring carrier 15 is driven into roller bearings 27.

large chain ring 18 and middle chain ring 17 are fixed onto chain ringcarrier 15.

the two rollers 34 are fixed onto chain ring carrier 15.

small chain ring 16 is fixed onto chain ring carrier 15.

washer 49 is introduced into outer spindle 8, then the two rollerbearings 48 are driven in.

the first needle roller bearing 51 is driven in, spacer 52 is inserted,the other needle roller bearing 51 is driven in, then sealing gasket 53.

outer spindle 8 is held vertically and screw 50 is introduced placed ona screwdriver in hole 54.

inner spindle 9 is introduced in outer spindle 8. Screw 50 is tightenedquite hard and plug 47 is put in place.

spacer 40 is introduced into eccentric member 26, then needle rollerbearing 45 is driven into the eccentric member until it touches thespacer. Sealing gasket 46 is also driven in. Spacer 40 is removed again.

lock-nut 29 is screwed against eccentric member 26.

the two spindles are introduced into eccentric member 26.

spacer 40 is introduced into eccentric member 26.

washer 44 is placed on outer spindle 8, the width thereof having beenpreviously adjusted, then roller bearings 41 and circlip 43.

the assembly is screwed into bottom bracket tube 2.

the assembly is unscrewed until eccentricity E of eccentric member 26 isdirected in the desired position, for example horizontally forwards.

lock-nut 29 is unscrewed to block eccentric member 26 on tube 2.

sealing gasket 42 is introduced into socket 38.

socket 38 is screwed into tube 2 and tightened quite hard.

the chain is put on one of chain rings 16 to 18.

the pedals are mounted on cranks 11 and 13.

cranks 11 and 13 are mounted on the profiled heads 55 and 56 of spindles8 and 9.

A particularly advantageous feature of crankset 1 consists in that thetwo diametrically opposite rollers 34, forming the articulations ofconnecting rods 21, 23 on chain ring carrier 15, are each disposedsubstantially facing the corresponding crank 11, 13. This means thateach radial arm 20, 22 is offset angularly with respect to thecorresponding crank, by an angle which is determined by the lengths ofthe connecting rod and the arm. This offsetting is preferably forwardsin the normal rotational direction of the crankset, in order to exerttraction on the connecting rod, but it could also be in the otherdirection. The advantage of this position of the anchorage points on thechain ring carrier is that, when the crank is directed forwards and thusproduces the greatest driving torque, the direction of the connectingrod is approximately perpendicular to the direction of eccentricity E,which allows the maximum torque to be transmitted in an optimum mannerto the chain ring carrier, as will be seen hereinafter. This advantageis largely preserved if the eccentricity is given a direction other thanhorizontal, as long as it is directed forwards.

FIG. 4 shows eight successive positions a-h of right crank 13, with itsradial arm 22, its connecting rod 23 and rollers 31 and 34 forming thearticulations of the connecting rod, for eight successive positionsspaced at 45° from chain ring carrier 15. If one assumes that thebicycle travels at a constant speed and the angular velocity of thechain ring carrier is thus constant, the eight positions are regularlyspaced in time. In FIG. 4, the angles of rotation δ of the chain ringcarrier and θ of the crank have their origin in the vertical linepassing through the corresponding axis of rotation 25, 10. The Figureshows the following dimensions:

    ______________________________________                                        Length of each arm 20, 22                                                                            R.sub.1  = 60 mm                                       Radius of anchorage point 34                                                                         R.sub.2  = 55 mm                                       on the chain ring carrier                                                     Eccentricity (horizontal)                                                                            E = 5 mm                                               Length of each connecting                                                                            B = 28 mm                                              rod 21, 23                                                                    Arm-crank offset       ζ = 27°                                    ______________________________________                                    

It will be noted that E=R₁ -R₂, so that the two corresponding circles 57and 58 are tangent. As a result, in the proximity of position a, wherethe crank is directed forwards and produces the maximum torque, theconnecting rod is substantially perpendicular to the radius of the twocircles and thus transmits the torque in an optimum manner, with minimumradial stresses.

The opposite positions a-e, b-f, c-g and d-h show simultaneousrespective positions of the two cranks. The angle between the two cranksis maximum in the position c-g close to the vertical, thus perpendicularto the direction of eccentricity E, which removes the dead centreposition in a known manner. During the rising trajectory of each crank,corresponding to positions d, e and f, connecting rod 23 is notperpendicular to radii R₁ and R₂, but this is not important since itdoes not then transmit any significant effort. Conversely, theconnecting rod is substantially perpendicular to the radii in thedescending trajectory of the crank (positions g, h, a and b), whichallows the direction of eccentricity to be modified by pivotingeccentric member 26, for example for adapting the gear crank to themorphology of the cyclist or to his personal position on the bicycle,without affecting the crankset performance.

FIG. 4 also shows that the arrangement of rollers 34, i.e. the anchoragepoints of connecting rods 21 and 23 on chain ring carrier 15 facing eachcrank 11 and 13, may be changed under certain conditions whilemaintaining the same kinematic and dynamic advantages. From the diagramof FIG. 4, let us assume that crank 13 is mounted in another orientationon its spindle 9, which means selecting another value for angle ξbetween the crank and the corresponding radial arm 22. For example, letus assume that in position a of the mechanism, horizontal crank 13 isdismantled and remounted vertically upwards, by acting alsosymmetrically with the other crank, this means adding 90° to ξ andremoving 90° from θ without changing any of the other parameters. Thechange in θ changes the direction of application of forces by thecyclist with respect to the crankset. It is thus sufficient to pivot thecrankset by 90° forwards in its tube 2 about axis 10 in order tore-establish the kinematic and dynamic conditions of FIG. 4.Eccentricity E then becomes vertical downwards, axis 25 being placedbelow axis 10. The general condition relative to the preferred positionof the articulations formed by rollers 34 is thus that, when the crankis situated in a horizontal forwards position, articulation 34 of thecorresponding connecting rod on chain ring carrier 15 must be inproximity to the radial plane passing through the two axes 10 and 25,thus in the same general direction as eccentricity E. An advantage ofthis arrangement is that right crank 13 can easily be placed in the sameradial plane as the two arms 20 and 22, resulting in a gain in the widthof the crankset and the spacing between the two pedals.

FIG. 5 shows the torque M applied to chain ring carrier 15 as a functionof the angle of rotation δ thereof, assuming that the cyclist exertssolely a descending vertical force of 600 N on the descending crank, thecranks having a standard length of 175 mm. Curve 60 represents thetorque in a conventional crankset, wherein the two cranks are attachedto the chain ring carrier. Curve 61 represents the torque in crankset 1according to the invention, in the arrangement of FIG. 4, i.e. witheccentricity E horizontal forwards. This curve is flatter than curve 60,i.e. the torque is more uniform over one revolution of the crankset. Theminimum torque 63, in the dead centre zone where torque 60 of theconventional crankset falls to zero, represents approximately 20% of themaximum torque. In practice, one knows that the minimum torque willoften be slightly higher, because a skilled cyclist nonetheless appliescertain horizontal or rising forces to the pedals.

Curve 64 represents the torque in crankset 1 when eccentricity E isdirected forwards at 30° above the horizontal. It will be noted that itis very close to curve 61 and has the same maximum and minimum values,i.e. such a pivot of eccentric member 26 does not affect the cranksetperformance when the forces applied to the pedals are vertical.Conversely, it allows the crankset kinematics to be adapted, inparticular the position of the zone in which the cranks are offset, tothe morphology of the cyclist and his position on the bicycle.

The diagram of FIG. 6 shows the evolution of the angular velocity ω ofthe cranks as a function of angle θ of right crank 13 for a constantspeed of chain ring carrier 15 (1 revolution per second) and thus of thebicycle, when eccentricity E is in a horizontal direction, thus in theconditions of curve 61 of FIG. 5. Curve 65 concerns right crank 13 andcurve 66 concerns left crank 11. The straight line 67 represents thevelocity of chain ring carrier 15.

It will be noted that each crank rotates more slowly when it descends,and more quickly when it rises. The speed of each crank variesprogressively, smoothly, and the minimum speed represents approximately86% of the maximum speed. This is important for the cyclist's comfortand facilitates endurance by avoiding imposing substantial accelerationsand decelerations on his legs.

In light of the preceding description, those skilled in the art willunderstand that the invention allows a crankset to be provided which isperfectly protected against external conditions, in particular, waterand dirt, without using bulky accessories such as an external housing.Moreover, the crankset can be completely assembled prior to introductioninto the bottom bracket tube, which guarantees secure and easy assemblyand also facilitates any disassembly. The offset position of arms 20 and22 with respect to the cranks, contrary to the prior art according to FRPatent No. 2 584 671 wherein such arms are situated facing the cranks,allows advantageous kinematics and optimum transmission of the torquefrom the cranks to the chain rings, without increasing the dimensionsand weight of the construction. If necessary, this arrangement alsoallows the right crank and the arm associated therewith to be made in asingle part, thereby allowing a substantial gain in the total width ofthe crankset. This arm is not then necessarily radial and can, inparticular, extend in a circumferential direction from the crank.

I claim:
 1. A crankset without a dead center position, including:a fixed bottom bracket tube; a hollow outer spindle rotatably mounted about a first axis by first bearings in said bottom bracket tube and attached to a first crank; an inner spindle rotatably mounted by second bearings coaxially in said outer spindle and attached to a second crank; sealing means for assuring sealed protection of said bearings as regards an exterior of said crankset; an output member rotatably mounted about a second axis parallel to and offset with respect to said first axis on an eccentric member fixed to said bottom bracket tube, said output member being intended for driving a mechanical transmission; and a first articulated linkage connecting said output member to one of the first crank and the outer spindle, and a second articulated linkage connecting said output member to one of the second crank and the inner spindle, wherein said sealing means include first sealing means, disposed around said outer spindle in said bottom bracket tube and protecting said first bearings as regards an exterior of said tube, and second sealing means, disposed in said outer spindle and protecting said second bearings as regards an exterior of said spindle, and wherein said second sealing means include an annular sealing gasket, which obturates an annular gap between said outer spindle and said inner spindle on the side of said second crank, and closing means which obturate in a sealed manner a central bore of said outer spindle on the side of said first crank.
 2. A crankset according to claim 1, wherein said eccentric member is adjustable by pivoting about said first axis to adjust the direction of its eccentricity.
 3. A crankset according to claim 2, wherein said eccentric member is screwed into said bottom bracket tube and carries a lock-nut arranged for blocking it against said tube.
 4. A crankset according to claim 1, wherein each of said articulated linkages includes a connecting rod having one end connected to an output member by a first articulation, the other end of said connecting rod being connected to one of the corresponding spindle and the corresponding crank by a second articulation, and wherein said first articulation is situated in proximity to a radial plane passing through said first and second axis when the corresponding crank is in a descending horizontal position.
 5. A crankset according to claim 4, wherein said first articulation is situated substantially facing the corresponding crank.
 6. A crankset according to claim 5, wherein each spindle is provided with a respective radial arm disposed on the exterior facing said output member and carrying said second articulation, said arm being offset angularly with respect to the corresponding crank.
 7. A crankset according to claim 4, wherein each spindle is provided with a respective radial arm disposed on the exterior facing said output member and carrying said second articulation, said arm being offset angularly with respect to the corresponding crank.
 8. A crankset according to claim 7, wherein each crank is removably mounted on the corresponding spindle.
 9. A crankset according to claim 4, wherein, in a vertical plane view, circles representing the trajectories of said first and second articulation of each connecting rod are tangent.
 10. A crankset according to claim 1, wherein said output member is a chain ring carrier on which one or more toothed chain rings are removably mounted. 